Automatic volume control circuit



Sept. 21, 1937. K. A. cHlTTlcK ET Al. 2,093,548

l v AQJTOMATIC VOLUME CONTROL CIRCUIT original Filed Nov. 14, 1932iwillim- 5,51 wherein there is shown theA circuit diagram of PatentedSept. 21, `1937 AUTIVIATICA VOLUME `CONTROL CIRCUIT Kenneth A. Chittickand Wendell L. Carlson, Haddonield, N. J., assignors toRadio Corpora-`tion of America, a corporation of Delaware origami @plantationNovemberfii, isea'ser'iai No.

642,544.v Dividedand this application Janu` ary 26, 1935, Serial No.3,546

12 claims. (o1. 250g-2o) Y Our present invention relates to a radioreceiver volume control circuit, and more particularly to a novel andimproved type` of manual volume control arrangement for aradio broadcastreceiver, the present application being a division of our applicationSerial No. 642,544, filed November 14,

One of the main objects of the present invention is to provide in aradio receiver, as of the broadcast type, a compound manual volumecontrol, the manual control functioning to reduce the radio frequencyamplification `about ten times during the first part ofthe controlactuation, and subsequently regulating volume substantially entirely by`variable `audio frequency gain.

Another object of 'theinvention is to provide in a radio receiver amanual volume control device which is adapted to predominantly vary `theradio frequency amplieation during the first part of its actuationfrommaximum to minimum volume, and subsequentlyto predominantly vary theaudio frequency transmission throughout the remainder of the controlactuation `until the 'minimum volume point is obtained.

Another object `of the invention is to provide in a radio receiver ofthe superheterodyne type equipped with an automatic volume controlcircuit which has a definite relation to the selectivity as well as the`sensitivity of the receiver,` a manual volume control instrumentalitywhich functions to change the radio frequency and intermediate frequencyamplification as well as the signal transmission between` the seconddetector output and the audiofrequency network.

Still other objects of the invention are to im-` prove generally thesimplicity and efficiency of volume control for radio receivers, andespecially to provide a superheterodyne type of receiver which not onlyemploys a highly eicient andreliable automatic volume control circuit,but also utilizes a manual volume control device which is economicallymanufactured and assembled in the receiver.

The novel features which we believe to be characteristic of ourinvention are set` forthin particularity in the appended claims, theinvention itself, however, as to both its organization and method ofoperationwill best be understood by reference to thefollowingdescription taken in connection with the drawing in which we have iindicated diagramrnatically a circuit' organization whereby ouryinvention may be carried into effect.

Referring now to the accompanying drawing,

' Patent 1,740,331 to a superheterodyne receiver embodying the presentinvention, the superheterodyne broadcast receiver shown includes the'usual' grounded signal collector, or antennacircuit A which iscoupled,as at M1, tothe input electrodes ofthe-firstradio-fre'- quencyamplifiertube I, the latter'tube beingv of the well known radio frequency pentode58type. 'Ihe tube has I.its anode circuit coupled, as at M2, to theinput electrodesof :the first detectorjthe latter being conventionallyshown"butl'it1 being clearly understood that the first detector tube mayalsofbe of the 58 type. 1 Then usuallocaloscillator circuit isconventionally represented, andl its coupling to the first'de'tector'isschematically shown, the construction `of the local oscillator "andfirst detector circuits being Well known'to those skilled in theart-,and a detailed explanation thereof being unnecessary for afproperunderstanding'of the presentuinvention. lf V i The output ofthe firstdetector, which includes theV desired intermediate .frequencyenergy isim'- pressed, as at lVb, upon `the inputcelectr'odeslof the`intermediate frequency amplifier Itube 2,1 which to.l one or moresuccessive "stages of 'audio fre quency amplification followed by'` anydesired type of reproducer, such asa loud speaker of the electrodynamictype. 1f: n

Theaforegoing general description of .the essential components of ,asuperheterodyne receiver are vwell known, and it'is, ladditionally,well.

known to those skilled in the artthat the rotors of the tuningcondensers di, ll', Il, Vmay-bermechanioally coupled, in any well knownmanner, for manipulation byl a uni-control device 5, shown in dottedlines. The condensers 4, 4', and d" are arranged toresonate the inputcircuits of the radio frequency amplier, the rst detector, and the localoscillator respectively, it being noted that the` rotors of each ofvthese condensers are grounded. Again, the input circuitof` theintermediate frequency amplifier tube is maintained xedly Atuned to thesame intermediate frequency as the output circuit ofy the rst' detectorand the output circuit of the intermediate frequency amplifier tube 2,and the input circuit of the second detector. The intermediate frequencymay be maintained constant over the tuning range by using a means as`disclosed in U. S. W. L. Carlson of December The automatic volumecontrol path includes the amplifier tube 6, preferably of the 58 or 5'7type, and a tube 1, of the 56 or equivalent type, the tube I beingarranged to function as a diode, or equivalent rectifier, by strappingthe control electrode to the anode. The output electrode, comprising thestrapped grid and anode, of tube 'I is connected by a lead 8 to thecontrol grid circuits of the radio frequency amplifier tube I, the firstdetector tube, and the intermediate frequency amplifier tube 2. Thecoupling between the anode circuit of amplifier 6 and the electrodecircuit of tube l, which coupling is designated by the referencecharacter Ms, is relatively great so as to respond to a broad frequencyband.

It will be now observed that the automatic volume control arrangementemployed in the present invention comprises a branch circuit in parallelwith the signal circuit, the grid of tube 6 being connected to the highpotential side of the resonant input circuit of the intermediatefrequency'amplier tube 2 through a path which includes the lead 9, thefixed condenser I0, the latter being also connected to ground through aresistor II. The condenser I0 is preferably given a magnitude of about300 mfd., and the resistor I I is desirably given a magnitude of about 2megohms. The usual direct current blocking condensers II are employed ineach of the grid circuits of the controlled tubes, and there have alsobeen shown the conventional self-biasing networks I2 in the groundedcathode legs of each of tubes 2 and 6.

It will now be pointed out that the present inventlon provides anautomatic volume control which has a very definite relation tosensitivity and selectivity. The volume control tube itself is a rectierof the two element type and has a special intermediate frequencyamplifier stage to drive it. This volume control is more effective thanvolume control arrangements of the prior art. Due to its action theradio frequency voltage applied to the second detector is substantiallyconstant for a signal of from 100 microvolts input to that of severalvolts. This regulation is obtained by effectively controlling the signalvoltage beyond the point in the circuit where the automatic volumecontrol is connected. The voltage to the automatic volume control tubehowever will not be constant. Such regulation in addition to beingdesirable from an entertainment viewpoint is also essential in thisreceiver due to the location of the manual volume control. Since thereis no danger of overload on the second detector grid, the manual volumecontrol C may therefore be located in the audio frequency circuit.

The automatic volume control network, in detail, comprises the lead 8from the control tube 1, resistors R1, R2, R3 and R4, Rs, R13; the lead8 being connected intermediate the resistors R1 and R2. 'I'he gridcircuit of the first detector stage is connected to a point intermediatethe resistors R2 and R3 through a lead I3 which includes in series aresistor R8. The grid circuit of the intermediate frequency amplifiertube is connected by a lead I4, and includes in series the resistor R13,to a point intermediate the resistors R3 and R4.

The automatic volume control arrangement functions in the followingmanner: The input signal'voltage for the intermediate frequencyamplifier is additionally applied to the amplifier tube 6 due to thegrids of both tubes being coupled together by means of the capacitor I0.The

output of the intermediate frequency amplifier tube 2 is applied to thesecond detector through a sharply tuned transformer. However, the outputof the volume control amplifier 6 is coupled to the volume control tubeI through a broadly tuned transformer Me. The location of the automaticvolume control, and coupling it in this manner is due to two reasons.

In the first place, too much selectivity ahead of the automatic volumecontrol is not desirable as it introduces excessive distortion andoverload as a station is tuned in. However, a certain amount ofselectivity is essential, otherwise the volume control will be caused tofunction by a local station when it is desired to tune in a weakerstation on an adjacent channel. The increased selectivity beyond theautomatic volume control in the signal circuit (transformer M4) addsmaterially to the apparent selectivity as well as the actual selectivitybecause the automatic volume control action does not tend to overcomethe reduction of signal strength to the second detector when tuning offresonance on transformer M4.

The volume control tube 1 possesses a linear rectifier action by virtueof the strapping of the grid and plate. The drop across resistors R2, R3and R4 gives the bias for the radio frequency tube I. 'I'he drop acrossresistors Ra and R4 comprises the grid voltage for the first detector,and that across resistor R4, the grid voltage for the intermediatefrequency amplifier tube 2. As the drop in these resistors is due to thesignal voltage applied to the volume control tube '1, and this voltageis in turn dependent on the bias of the tube I, rst detector tube, andtube 2, an automatic action is obtained. The reason for the greatervoltage applied to the radio frequency tube I and first detector thanthat applied to the intermediate frequency amplifier tube 2 is tofurther prevent overloading of these tubes on the side of a strongcarrier.

The filter resistors Ra and R13 preferably have a magnitude of about100,000 ohms each, the blocking condensers II, and the by-passcondensers I I' each having magnitudes of 0.1 mid. For purposes ofillustration it may be stated that the resistor R1 may have a magitudeof 500,000 ohms; the resistor R2 may have a value of 400,- 000 ohms; theresistor R3 may be 100,000 ohms; and the resistor R4 may have amagnitude of 400,000 ohms. The resistor R9 is connected in the cathodelead I5 of the first detector stage, the cathode lead I6 of the tube Ibeing connected, with the lead I5, to a common lead I'I which isgrounded through a resistor Ria.

One terminal of the resistor Ria is connected to an adjustable tap Awhich is adapted to function as a manual volume control device for theradio frequency section of the receiver. The tap A is mechanicallycoupled to the adjustable tap C of the audio frequency manual volumecontrol resistor R by means shown in dotted lines, and designated by thereference numeral I8. The resistor R9 furnishes self-bias for the gridof the first detector tube, and the resistor may have a magnitude ofabout 2,500 ohms, the resistor R14 which furnishes self-bias for thegrid of the amplifier tube 6 having a magnitude of about 1,500 ohms,while the self-bias resistor R15 for the tube 2 may have a value ofabout 2,500 ohms. The radio frequency volume control resistor Ria mayhave a value of some 400 ohms.

The positive potential supply sources for the screen grids and anode ofthe tube I, the first `301",degrees ofthe angular movement ofthe manualdetectortube, the tube `2, the tube 6 and the second detector tube arenot shown. These po- `tential sources are omitted to preserve simplicityof description, `but it` is understood that the pliedito the`detectoriis fed' through the coupling reactor L1,1' and the audiocomponent` passes through'the f0.5 mfd. coupling capacitor C1.` Themanual audio volume control is located between the second detectorandthe succeeding audio frequency amplifier stage, and functionsfto `re-`duce the voltage applied tothe primary of the inter-stage transformerM5. It is pointed` out i i that the resistorv R` comprises only onesection ofthe manual volume control I8.

f Actually, there are two sections, the other beand first detectorlcathodes and varying'the over-l all' sensitivity.` "The controlprevents'all noises and si'gnalsiof a very weak'character from beingreceived, and only functions over the last twenty volume ctintrol;`However`,'if such signals are desired it is only necessary to advancethe volume control the usual manner to its maximum position. 'In otherwords, the resistors Ria and R are arranged with respect to the commonmechanical drive is so that the tap iifduring une` erst twenty degreesof adjustmentjvaries the magnitude'of the resistor Ria, and-during theremainder of the adjustment of the manualdrive I84 variesv only themagnitude ofthe resistor R;

It should be noted `thatthe automatic volume control plus the `specialintermediate frequency amplifier provides a radio frequency voltage on rthesecond detector which is substantially con- `Stant between 9 and l2volts for ahsignal of from 10 microvolts to several volts. ,With thisarrangement, there is no danger of the second detector overloading,` andaccordinglythe volume control means may be placed in the audio frequencycircuit. For the purposeof reducing the extreme sensitivity, the manualautomatic volume control means operates for about 2O degrees'in `thecircuit.

` `a definite relation between the operation and the radio` frequencycircuit to reduce the sensi- 1 tivity to normal, then the audiofrequency 'volume ,"55. Ycontrol becomes effective and the volume may bearrangement of the manual Volume control and the functioning andconstruction of the automatic volume control, it being pointed out againthat by virtue of the automatic volume control arrangement, the mainportion of the manual volume control may be disposed at the audiofrequency section of the radio receiver,

Noise between stations is effectively reduced without seriouslycompromising the automatic volume control by means of the compoundmanual volume control disclosed herein which functions to reduce `theradio frequency gain about'ten times during the first part of thecontrol rotation, and later regulates volume entirely by Variable. audiogain. The noise between stations may be further reduced by employing afixed bias on the seconddetector, represented` merely for pur,; poses ofillustration by the source 2| in Fig. l, substantially greater than thevalue usually employed. The automatic volume control circuit of Fig. 1is characterized by its freedom fromobjectionable time lag; freedomfromdistortion of the low audio frequenciesyand its lackof`susceptibility to iiutter or motor-boating. I

While we haveindicated anddescribed a system for carrying our inventioninto effect, it will be apparent to'one skilled in the art that ourin-zvention is by no means limited `to` the particu-k lar organization.shown and described, butthat manymodiiications `may be made withoutdeparting from thescopefof our invention, as set 'f forth in theappended claims.

Whatwe claimis: .i j'

1. In combination with a high frequency-ampli- Iier whose gain is to becontrolled, a rectierifor the high frequency ampliiier'output, means fori coupling the high frequency amplifier to the rectiiier input, a deviceof asymmetric conductivity, a second high frequency amplifier coupleditosaid device, means for-coupling the output of the first amplifier to theinput of the second amplifier and l an automatic volume controlarrangement including a direct current potential connectiongbetween saiddevice and a gainfcontrol electrode of said iirst amplifier, means foradjusting the magnitude of the output of the-'rectier,\means foradjusting the conductivity of the vfirst amplifier,

`and a common manually operable means for conamplifier and anautomaticvolume control arrangement for maintaining the signal input tothe detector substantially constant between 9 and i2 volts for a signalof from 10v microvolts to several volts, a compound manual volumecontrol device for reducingfnoise between stations without substantiallyaffecting the action of said autoi matic control, saiddevice'including aresistor in the radio amplifier spacev current path, a resistor couplingthe detector and audio amplifier, and

means for successively varying the operativevalues of said-resistors.

3. In a radio receiver of a 'type including Va radio frequencyamplifier, aV detector,an audio'V frequency amplifier'` and an automaticvolume control'arrangement formaintaining the signal input to thedetector substantially constant over a relatively wide range of signalvoltage variation, a compound manual volume control device for reducingnoise between stations without substantially affecting the action ofsaid automatic control, said device including a resistor in the radioamplifier space current path, a resistor coupling the detector and audioamplifier, and means for successively varying the operative values yofsaid resistors, the resistors being so related that variation of thefirst resistor results in a decrease ofY gain of said radio amplifier ofabout ten times.

4. In a radio receiver of a type provided with a'tuned radio frequencyamplifier, a demodulator and an audio frequency utilization network,

means for varying the gain of the radio frequency amplifier, means forvarying the transmission of demodulated'signal energyv between thedemodulator and said utilization network, and a manually adjustablemeans for regulating the adjustments of said two varying' means in amanner Such that the radio frequency amplifier gain is predominantlyvaried during a portion of the actuation of said manually adjustablemeans, and thel demodulated signal transmission is predominantly variedduring the remaining portion of the actuation of the manually adjustablemeans.

5. In a radio receiver of a type provided with a tuned radio frequencyamplifier, a demodulator and an audio frequency utilization network,means for varying the gain of the radio frequency amplifier, means forvarying the transmission of the demodulated signal energy between thedemodulator and said utilization network, and a manually adjustablemeans for' regulating the adjustments of said two varying means in sucha manner that the radio frequency amplifier gain andsaid demodulatedsignal transmission are successively varied.`

6. In combination, a tuned radio frequency amplifier, a detector, anaudio frequency amplifier, a manual volume control device including avariable resistor disposed in the cathode circuit of said radiofrequency amplifier, a variable resistor being connected across thedemodulator output, and a common adjusting means mechanically coupledwith said two variable resistors for controlling the adjustments madethereto in a predetermined successive order.

7. In a superheterodyne receiver of the type including at least onetuned radio frequency amplifier, a first detector, second detector and afollowing audio frequency utilization network, a volume control devicecomprising means for varying the potential difference between the inputelectrodes of said radio frequency network, said means similarly beingarranged to vary the potential difference between the input electrodesof said first detector, means for varying the signal f transmissionefficiency between the second detector and said utilization network, anda manually adjustable device mechanically coupling said two means insuch a manner as to regulate the adjustments made thereto in apredetermined successive order. Y

8. In a radio receiver provided with a high frequency amplifier whosegain is to be controlled and a r-ectifler for the high frequencyamplifier output, means for adjusting the magnitude of the output of therectifier, means for adjusting the gain of said amplifier, and a commonmanually operable means for controlling both said adjusting means in apredetermined successive manner.

9. In a radio receiver of a type including a radio frequency amplifier,demodulator and an audio frequency amplifier, a compound manual volumecontrol device for reducing noise between stations, said deviceincluding a resistor in the radio frequency amplifier space currentpath, a resistor coupling the demodulator and audio amplifier, and meansfor successively varying the operative values of said resistors.

'10. In a radio receiver of a type including a radio frequencyamplifier, a detector and. an audio frequency amplifier, a manual volumecontrol device for reducing noise between stations, said deviceincluding a resistor in the radio frequency amplifier space currentpath, a resistor coupling the detector and audio amplifier, and meansfor successively varying the operative values of said resistors, theresistors being so related that variation of said last means duringsubstantially the first 20 of its adjustment varies solely the magnitudeof said first resistor, and during the remainder of the adjustmentthereof varies solely the magnitude of the said second resistor in orderto reduce the sensitivity of the receiver from maximum to minimum.

11. In a superheterodyne receiver of the type including a radiofrequency amplifier, frequency changer, intermediate frequencyamplifier, second detector and means for tuning the radio amplifier andfrequency changer to select different signal carrier frequencies, anautomatic volume control network including a diode rectifier, and adirect current potential connection between the rectifier anode and aninput electrode of at least each of said two amplifiers, a selectivenetwork between said intermediate amplifier output and the seconddetector, a second selective network between the intermediate amplifierinput and the diode, both said selective networks being tuned to theintermediate frequency, the selectivity of the first network beingsufficiently greater than that of the second network to minimizeoverloading of the second detector on the side of a strong signalcarrier frequency when tuning the receiver through a carrier frequency,and a manual volume control device arranged to supplement the automaticvolume control network for the reduction of undesired noises when tuningbetween carrier frequencies, said device including a single adjustableresistive means for successively varying the gain of said radioamplifier and the second detector output.

12. In a wave transmission system of the type provided with a wavetransmission tube feeding a demodulator, the improvement which comprisesa device for adjusting the gain of the transmission tube, a seconddevice for adjusting the magnitude of the demodulator output, and acommon means for regulating the adjustments of said two devices in apredetermined successive order such that the said gain is predominantlyvaried during a portion of the actuation of the common means, and thedemodulator outputmagnitude is predominantly varied during anotherportion of the actuation of the said common means.

WENDELL L. CARLSON. KENNETH A. CHI'ITICK.

